astronomy chapter 2

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astronomy chapter 2
2013-08-25 18:50:58
astronomy chapter heidili

astro 100
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  1. positional astronomy
    the study of the  positions of objects in the sky and how these positions change
  2. constellations
    groupings of stars
  3. diurnal motion
    daily motion of stars
  4. what happens if you follow a particular star on successive eveings
    you will find that it rises approximately 4 minutes earlier each night or 2 hours earlier each month
  5. celestial sphere
    imaginary object that has no basis in physical reality. nonetheless the sphere remains a useful too fo positional astronomy.
  6. celestial equator
    divides the sky into northern and southern hemispheres
  7. north and south celestial pole
    the two celestial poles where Earth's axis of rotation intersects the celestial sphere.
  8. north celestial pole
    the star Polaris is less than 1 degree away from the north celestial pole which is why it is called the North Star
  9. zenith
    point in the sky directly overhead an observer anywhere on Earth
  10. circumpolar
    stars that are never rising or setting
  11. ecliptic plane
    the plane of Earth's orbit around the sun
  12. equinox
    the ecliptic and the celestial equator intersect at only two points which are exactly opposite each other on the celestial sphere. 

    when sun appears at either of these points day and night are each about 12 hours long
  13. vernal equinox
    On about March 21 of each year the Sun passes northward across the celestial equator. This marks the beginning of spring in northern hemisphere
  14. autumnal equinox
    On September 22 the Sun moves southward across the celestial equator at the autumnal  equinox, marking the moment when fall begins in the northern hemisphere.
  15. summer solstice
    between the vernal and autumnal equinoxes lie. the point on the ecliptic farthest north of the celestial equator is called the summer solstice.
  16. winter solstice
    at the beginning of the northern hemisphere's winter the sun is farthest south of the celestial equator
  17. Tropic of Capricorn and the Tropic of Cancer
    Between the two tropics at 23.5 degrees south lat and the latter 23.5 degrees north, the Sun is at zenith.
  18. precession
    caused by the gravitational pull of th eSun and the Moon on Earth's equatorial bulge. It causes the positions of the equinoxes and celestial poles to shift slowly.
  19. zodiac
    The moons path varies somewhat from one month to the next but always remains wtihin the band called zodiac which extends 8 degrees on either side of the ecliptic.
  20. precession of the equinoxes
    The intersections of the celestial equator and the ecliptic define the equinoxes so these key locations in the sky also shift slowly from year to year
  21. How do stars appear to move over the course of the night as seen from the north pole? As seen from the equator? Why are these two motions different?
    At the north pole all stars are circumpolar. Stars on the celestial equator would make a 360 path following the horizon. From the equator all stars rise and set. The 90 degree difference in latitude is responsible for the difference.
  22. How are the four points (autumnal, vernal, summer/ winter solstice) related to the ecliptic and celestial equator?
    The equinoxes are the points where the ecliptic intersects the equator and the solstices are 90 degrees from the equinoxes along the ecliptic